7 Evolution and Ecology
Explore how evolution changes populations over generations, how ecological conditions shape that change, and how evolving species influence their communities.
happens in populations
is a change in the inherited characteristics of a population across generations, often measured as a change in allele frequencies. The distinction between individuals and populations is important: an individual may grow or change during its lifetime, but describes inherited changes across generations in a population.
How shapes
occurs when individuals vary in heritable traits and those differences affect survival or reproductive success. Individuals with greater tend to contribute more surviving offspring to the next generation, so the alleles associated with their traits may become more common.
For example, a population of insects may contain heritable variation in coloration. If darker habitat makes dark-colored insects harder for predators to see, those insects may survive and reproduce more often. The environment does not create useful variation because organisms need it: selection acts on variation already present. Mutation introduces new alleles, while sexual reproduction reshuffles existing ones.
An is a heritable trait shaped by that improves survival or reproduction in a particular environment. A trait's advantage depends on conditions and can change when the environment changes. is not goal-directed and does not produce perfect organisms; it can favor an average trait, one extreme, or multiple distinct forms.
Other processes of evolutionary change
is not the only process that changes populations. changes allele frequencies by chance and can have a particularly strong effect in small populations. moves alleles between populations when individuals or their reproductive cells migrate. Mutation, , and can all affect genetic variation and influence how populations respond to selection.
Takeaway: Population change reflects both selection and other evolutionary processes, including chance and migration.
How populations diverge into species
is the formation of new species. It commonly involves reproductive isolation: populations no longer interbreed successfully or produce fertile offspring.
In , a geographic barrier separates populations and reduces . Mutation, , and may then cause the separated populations to diverge. If they meet again, differences in mating behavior, timing, or biology may prevent successful reproduction.
In , reproductive isolation develops without geographic separation. Ecological differences can contribute to either path: populations that use different food sources or breed in different habitats may experience different selection pressures. Over time, adaptations to those conditions and changes that reduce interbreeding can increase divergence.
Ecological relationships and
Interactions among organisms create selection pressures. Predators can favor prey with stronger defenses or better camouflage, while prey can favor predators that find or capture them more effectively. Competition for limited food, light, nesting sites, or other resources can favor traits that improve resource use. These traits may also affect where a species can live and which other species it encounters.
When two or more species exert reciprocal selection on one another, they may coevolve. For example, a flowering plant and its pollinator may each evolve traits that affect the other's feeding or reproduction. does not necessarily mean that both species benefit equally or that their relationship is perfectly matched. Interactions such as predator–prey and host–parasite relationships can involve conflict.
Ecology and therefore continually influence one another. Changes in climate, resources, competitors, or predators can alter which traits are favored. Evolutionary change in a species can, in turn, alter its interactions and its role in the ecosystem.